INSULIN INHIBITS SEROTONIN-INDUCED CA2-MUSCLE( INFLUX IN VASCULAR SMOOTH)

Background Insulin in physiological concentrations attenuates the agon ist-induced intracellular Ca2+ ([Ca2+](i)) transient and inhibits cont raction in individual nonproliferated cultured canine femoral artery v ascular smooth muscle cells (VSMCs). In the present study, we wished t o define the effects of insulin on individual components of Ca2+ trans port in vascular smooth muscle. Methods and Results Insulin (40 mu U/m L) attenuated the 5-hydroxytryptamine (5-HT, serotonin; 10(-5) mol/L)- induced [Ca2+](i) transient (measured by fura 2 fluorescence) in prima ry confluent canine femoral artery VSMCs in the presence of extracellu lar Ca2+. In Ca2+-free media, the 5-HT-induced [Ca2+](i) transient was reduced by 42% and was not affected by insulin. This finding suggeste d that insulin inhibits 5-HT-induced Ca2+ influx but does not affect s arcolemmal Ca2+ efflux or Ca2+ release from intracellular stores. In s upport of those conclusions, we found that insulin inhibited the 5-HT- induced component of Mn2+ (a Ca2+ surrogate) influx (measured by fura 2 fluorescence quenching at the Ca2+ isosbestic excitation wavelength) . In addition, 5-HT stimulated the rates of Ca-45(2+) efflux from inta ct cells (a measure of sarcolemmal Ca2+ efflux) and from saponin-perme abilized cells (a measure of Ca2+ release from intracellular stores), but insulin did not affect these rates of Ca-45(2+) efflux. Conclusion s We conclude that a physiological insulin concentration attenuates th e 5-HT-induced [Ca2+](i) transient in confluent primary cultured canin e femoral artery VSMCs by inhibiting the 5-HT-induced component of Ca2 + influx but not by affecting sarcolemmal Ca2+ efflux or Ca2+ release from intracellular stores.